For winter tires for use on icy and snowy road surfaces, performance on icy and snowy roads—specifically, superior braking ability on icy and snowy roads—is demanded in addition to dry grip performance, wet grip performance, and wear resistance.
To satisfy such a demand, for example, Japanese Unexamined Patent Application Publication No. 2010-270207A proposes “a rubber composition for a tire tread including a diene rubber component and silica and carbon black, the diene rubber component including: (A) from 30 to 80 mass % of a hydroxy group-containing aromatic vinyl-conjugated diene copolymer containing from 20 to 30 mass % of aromatic vinyl units and from 0.1 to 10 mass % of isoprene units, and having an amount of vinyl bonds in a conjugated diene part of 40 to 60 mol %; (B) from 10 to 50 mass % of a high-cis butadiene rubber having 90 mol % or greater of cis-1,4 bond content; and (C) from 10 to 50 mass % of natural rubber; a total amount of silica and carbon black being from 90 to 150 parts by mass per 100 parts by mass of the diene rubber component” (claim 1), and also describes a winter tire including this rubber composition for a tread (claim 5 and claim 6).
When the inventors of the present technology studied the rubber composition for tire treads described in Japanese Unexamined Patent Application Publication No. 2010-270207A, the inventors found that the wet grip performance (hereinafter, simply abbreviated as “wet performance”) and/or performance on icy and snowy roads of the produced tire may be poor depending on the type and compounded amount of diene rubber.